Multiple lock systems are used to allow access to an area by multiple users while preventing access to unauthorized persons. Such systems may be used, for example, on property with oil and gas leases, hunting leases, or wireless communications towers. One advantage of multiple lock systems over a single lock system is that a user authorized to access multiple areas may use locks with the same key for each area, eliminating the need for that user to carry multiple keys and reducing confusion over which key provides access to which area. Another advantage is that when a user is no longer authorized to access the area, the user's lock can be replaced or eliminated, and the distribution of new keys to all of the other users is not required.
One simple prior known multiple lock system uses a chain around a gatepost and a post on a gate secured by multiple padlocks linked in series with each user having their own padlock and key. One disadvantage of this system is that a user may bypass one or more locks when resecuring the chain, thereby preventing access to the users of the bypassed locks. Another disadvantage is that one user can remove the whole system. Detection of an unauthorized lock, added by cutting the chain and inserting the lock, is very difficult with this system.
U.S. Pat. No. 7,503,194 to the present applicant discloses a multiple padlock system with links that encircle a gatepost and links that encircle a post of a gate. This system and the chain system described above generally require an accessible gatepost and an accessible post on the gate. U.S. Pat. No. 6,857,299 to the present applicant discloses a multiple padlock system with a plurality of push bolts that each accept a padlock, and a sliding bar that is released by removing a padlock and pressing the associated push bolt. The number of push bolts can be easily changed by a master user, and the system can be used with almost any type of gates and with doors.